The present invention relates to a matrix and a process for the production of a package trough having at least one undercut.
Packages, particularly for foods, are becoming increasingly important today. The foods are placed in a so-called package trough and the package trough is then closed with a covering film.
As a rule, the package troughs are semi-continuously produced in so-called deep drawing stations of packaging machines. To this end, a film from which the package trough is produced is fed over a matrix of the deep drawing station, fixed there, optionally heated and then deep-drawn into the matrix using pressure, for example. The matrix is then lowered and the finished package trough is released from the matrix. As soon as the matrix has been lowered such that it is beneath the freshly produced package trough, the latter is moved on by the length of one package trough. The matrix is then raised again and the next package trough is deep-drawn.
For the packaging industry, so-called stand-up packages are of very special interest because they do not lie flat on the shelf but stand upright and thus provide a large presentation surface. Stand-up packages do not rest on the underside of the package trough but stand on a narrow side part of the package trough, i.e. the covering film on this package is roughly perpendicular to the bearing surface on which the package stands. For these packages, the package trough must have, in addition to the cut edge, a second standing surface on which the stand-up package firmly stands. This standing surface can be realized, for instance, in the form of an undercut whose lowest point must be on roughly the same level as the cut edge and thus does not tip backwards when it stands on its side.
However, such an undercut creates difficulties during the mold release of the package trough from the matrix after deep drawing because the undercut of the package trough is pressed against the matrix when the latter is lowered, thereby being either dented or even destroyed.
Therefore, a number of attempts have been made to provide devices for the production of package troughs having an undercut wherein the undercut is not damaged during mold release. EP 0,538,570, for example, teaches that the matrix during release is guided not vertically downwards but parallel to the tilted side face of the undercut. In this way it is possible to produce package troughs having undercuts transverse to the direction of package trough feed. The disadvantage of this procedure is that the movement of the matrix during release can only be realized with a relatively complex drive. Furthermore, this device can only be used for producing package troughs having an undercut transverse to the direction of package trough feed.